include <bits/stdc++.h>

using namespace std; int a[10006];

int main() {

int n;
scanf("%d", &n);
if(n==0){
	cout<<"0.00";
	return 0;
}
for (int i = 0; i < n; i++) {
	scanf("%d", &a[i]);
}
sort(a, a + n);
int ans = 0;
for (int i = 0; i < n - 1; i++) {
	ans += a[i] * (n - i - 1);
}
//cout << ans << endl;
double t = ans * 1.0 / n * 1.0;
printf("%.2lf", t);
return 0;

}